/**
 * Created by Administrator on 2017/4/17.
 */
function myEvent(obj,ev,fn){
  if(obj.attachEvent){
    obj.attachEvent('on'+ev,fn);
  }else{
    obj.addEventListener(ev,fn,false);
  }
}
myEvent(window,'load',function(){
  var oRTT=document.getElementById('rtt');
  var pH=document.documentElement.clientHeight;
  var timer=null;
  var scrollTop;
  window.onscroll=function(){
    scrollTop=document.documentElement.scrollTop||document.body.scrollTop;
    if(scrollTop>=pH){
      oRTT.style.display='block';
    }else{
      oRTT.style.display='none';
    }
    return scrollTop;
  };
  oRTT.onclick=function(){
    clearInterval(timer);
    timer=setInterval(function(){
      var now=scrollTop;
      var speed=(0-now)/10;
      speed=speed>0?Math.ceil(speed):Math.floor(speed);
      if(scrollTop==0){
        clearInterval(timer);
      }
      document.documentElement.scrollTop=scrollTop+speed;
      document.body.scrollTop=scrollTop+speed;
    }, 30);
  }
});
















